1. Field of the Invention
This invention is generally directed to medical implant devices and more specifically to implant devices which are specifically designed for the treatment of scoliosis and wherein the devices include a pair of generally parallel rod members which are reinforced by cross or spacer members that are adjustable to permit varied spacing between the spacer members to thereby both facilitate the placement of the implant and the surgical wiring of the implant to the patient's vertebrae and wherein the spacer members are positively retained in adjusted relationship with respect to the rod members after being adjusted along the length thereof. The implant devices of the present invention are designed to facilitate spinal support while allowing interchangability of components to thereby reduce implant costs and are also designed to reduce compression stress to the spinal column to thereby alleviate the possibility of neurologicly adverse affect to the medulla of the spine, such as disc compression or cutting off blood supply through the spinal column and thereby eliminates the chance for patient paralysis.
2. History of the Related Art
Scoliosis is a disease which mainly appears in young children during their growth years and the cause of which is unknown. The disease causes a normal spine to twist around itself and bend towards one of the sides and at the same time towards the front or back of a patient. In this respect, scoliosis is a tridimensional deformity of the spine which requires that any type of implant device be capable of correcting or normalizing the proper spinal alignment not only in the frontal plane, but also in the sagittal and axial planes of the patient's back.
Mild scoliosis may be treated by the use of special braces which can be worn exteriorly, however the disease can reach magnitudes which require surgical implantation of frames or braces to realign the vertebrae of the spine.
Early implantation devices incorporated a generally round stainless steel bar which was placed along the length of the spine to which the vertebrae were tied in order to correct the alignment of the vertebrae along the frontal plane. Although this type of device gained early acceptance it did not correct the total problem with spinal alignment as it did not deal with the sagittal and axial deviations of the spinal column.
Subsequent implant devices were developed which introduced the use of sublaminar wiring which incorporated stainless steel wires which passed through the back part of each vertebrae and which were then tied to two L-shaped stainless steel rods placed on either side of the spine. This type of device had the additional advantage of providing lateral compression and improved correction in the frontal plane. Unfortunately, this type of device does not provide sufficient stability and thus have not been widely accepted. Further development led to the formation of a rectangular rod-like frame to which the steel wires could be attached. This type of device had the effect of stabilizing the ends of the rods and therefore formed a more rigid structure. Unfortunately, when the length of the rods became excessive the rods themselves, which extend along the length of the spine, would have a tendency to collapse towards one another along their intermediate length thereby reducing the effectiveness of the device during patient treatment.
Further developments were made in spinal implantation devices such as disclosed in U.S. Pat. No. 4,686,970 to Dove et al.. This type of device modified the rectangular frame so as to provide generally V-shaped cross members for connecting the bars which extend along a patient's spine. With the device, wire ties were utilized to secure the vertebrae to the corners of the wire frame with the wires being directed to the corners by the tapered V-shaped cross members. Unfortunately, this type of structure has not proven to be sufficiently rigid to allow the best correction of the deformity and because that when the bar elements exceed a predetermined length it is possible for the side bars to collapse relative to one another during patient treatment. Further, during patient treatment it has been noted that in some instances the use of V-shaped cross members at the level of the thoracic spine produce a sensitive protruding lump under the skin that is not always well tolerated. Rigidity of an implant device is a desired property that will facilitate the correction of the deformity but reposition of the deformed spine to its normal position can lead to crimping of the vertebrae against each other forcing the spinal disc to protrude.
Dove et al. also discloses a modified device for treating children during their growth years. The modified device includes a frame-like member which is extensible in two sections so that the frame would theoretically lengthen as the length of the spinal column of the patient grew during the patient's growth years. Unfortunately, this type of device has not proven effective as body tissues adhere to both of the telescoping portions of the frame thereby prohibiting any spontaneous telescoping movement once the device has been implanted for any significant period of time. Further, even if movement was allowed, the movement is unrestricted between the two ends of the interfitting frame members. Undesirable movement of the frame members could result in shifting of the frame elements along the longitudinal axis of the spine with such shifting thereby allowing the collapse of the corrected spine.
Further improvements have been made in spinal implant devices and are disclosed in U.S. Pat. Nos. 4,738,251 issued Apr. 19, 1988 and entitled Correcting Devices for Spine Pathology and 4,875,471 issued Oct. 24, 1989 and entitled Device for Correcting Deformities of the Spine, both issued to the applicant of the present invention. In the earlier patent a device was disclosed which included a pair of elongated rod-like members which extended along the length of the deformed portion of the spine and which were connected by curved end portions which were designed to define a radius of curvature continuously from end-to-end and which therefore differed from the V-shaped cross members which were utilized in the Dove et al. patent. The implant device further included outwardly extending hook members which were positioned along each of the cross members and along each of the side rod members adjacent each cross member for purposes of facilitating the anchorage of stainless steel wires utilized to secure the vertebrae to the frame of the implant device. In the latter patent it was recognized that when spacer members were only provided adjacent the ends of the elongated rod members which extended along the deformed length of the patient's spinal column that the rods would tend to collapse relative to one another thereby not providing proper support for the vertebrae which were tied to the implant frame. Therefore, it was recognized that at specifically spaced points it was necessary to provide arcuate intermediate spacer members to thereby reinforce the elongated rod members to provide a more rigid overall structure. With this device, the frame is reinforced and is rigid in the frontal plane of the patient's spinal column, however the frame may be bent utilizing specially designed tools to reproduce the physiologic curves of the sagittal plane of the patient's spinal column. Thereafter, the frame may be progressively wired to the spine in such a manner that the wires interact with the frame so that the frame and wires concurrently react to correct the tridimensional deformity of the spine. Utilizing the implant device disclosed in U.S. Pat. No. 4,875,471 the curved cross or spacer members which join the elongated bar members of the implant frame effectively retain such bars in parallel relationship along their entire length thereby reinforcing the angle of correction of the spine in the sagittal plane. Further strength is imparted to the frame by forming the elongated rod members with a rectangular cross section as opposed to a round cross section as was traditionally utilized in implant frames.
Unfortunately, although the prior structures developed by the applicant of the present invention are believed to be significant advances in spinal implant technology, it has been recognized that such implants have features which limit their applicability. Generally, implant frames have not been designed to permit realignment of their reinforcing members during surgery, thus allowing the reinforcing strength of the spacer or cross members to be selectively applied at various points along the length of the implant frames. Thus, when rigid frames having rigid cross pieces are applied it is possible that the vertebrae may be drawn into a compact relationship with respect to one another due to the fixed components of the frame member. That is, when the spinal column is attached so that the normal vertebrae on either side of the deformed spinal section are wired to the endmost cross members associated with a rigid frame, the deformed vertebrae and disc which are intermediate must collapse into a linear space defined by the length of the frame. However, the spine itself is generally arcuately curved and therefore defines a dimension which is greater in length than the length defined by the frame. Should the vertebrae and disc become compressed it is possible that the disc space could close too much and cutoff blood supply by compression of the medulla. Such a cutoff of blood supply can result in patient paralysis.
A further disadvantage of prior art spinal implant frames is that they are extremely expensive to produce as each rigid frame must be manufactured in given dimensions i.e. lengths and/or widths, depending upon the size of the patient to be treated. Currently, there may be as many as 43 models of a given implantation frame which must be chosen to suit patients Again, as the frames are not adjustable, separate frames must be retained in inventory thereby significantly increasing treatment costs This procedure is further complicated in that an additional set of 43 models are provided for children. Therefore, prior art implants have not been designed to be universally applied nor have not been designed to allow the interchange of components so as to facilitate the formation of a rigid frame for each patient.
An additional example of prior art spinal implantation device is disclosed in Soviet Union patent 1063404 of Dec. 30, 1983.